Conventional methods of this kind for controlling an actuator, particularly for hydraulic actuators of the type indicated at the outset, are used for actuating valves such as the gas-exchange valves of an internal combustion engine or of a compressor, or for actuating flaps like, for example, rapid intake-manifold flaps in the intake manifold of a cylinder of an internal combustion engine, or for actuating other mechanisms. Such a hydraulic valve actuator is driven as a function of various operating parameters of the engine with the aid of an electronic control unit generally controlled by software. In this context, suitable drive variables, i.e., setpoint values for the necessary actuator drive signals are calculated based on control setpoint selections of a gas-exchange valve, e.g., for lift and timing, taking system state variables such as supply voltage, combustion-chamber pressure, hydraulic pressure and temperature into account, and the drive signals are generated in accordance with these setpoint values.
In the case of a hydraulic actuator described, for example, in German Patent Application No. DE 10 2004 022 447 A1, which is used in an electrohydraulic, camshaft-free positioning system for gas-exchange valves (EHVC), one drive signal each, made up of at least one pulse, is needed for controlling a control valve (MV1) on the high-pressure side determining the opening operation of an EHVC actuator, and for controlling a control valve (MV2) on the low-pressure side responsible for the closing operation. In this case, a single drive pulse determines the instant and duration for an opening of the control valve on the high-pressure side or for a closing of the control valve on the low-pressure side.
In this conventional EHVC system, in principle, lift and timing as well as opening velocity and closing velocity of the gas-exchange valves of an internal combustion engine are able to be freely programmed. This permits a flexible control of the gas exchange of the internal combustion engine, whereby the operational performance of the internal combustion engine, as well as its specific fuel consumption and vehicle emissions can be improved.
In principle, a method is able to be implemented for controlling a hydraulic valve actuator without feedback about the positioning operations themselves, that is, as a pure open-loop control. Suitable methods and control functions for controlling the lift of a hydraulic actuator are described in German Patent Applications DE 10 2005 002 385 A1 and DE 10 2005 002 384 A1.
A general disadvantage of these conventional design approaches is that they have to rely on a very good prediction of the possible actuator progressions, and therefore involve a high modeling and/or application expenditure in order to achieve the required actuator precision. The high expenditure relates primarily to the sufficiently accurate description of the multitude of dependencies, in connection with which influences such as oil pressure, oil temperature, viscosity and gas forces must be taken into account. In part, they are rapidly changeable, such as the oil pressure, and/or are difficult to model, like the gas forces, for instance.
In this problem area, which relates in the same way to other conventional camshaft-free valve controls as well, conventional design approaches start out from a feedback about a positioning operation. A suitable transducer is needed for that purpose.
German Patent No. DE 198 39 732 C2 describes a piezoelectric-hydraulic actuator for a gas-exchange valve, in which an electronic travel transducer is assigned to the actuator piston.
German Patent No. DE 199 18 095 C1 describes a circuit for controlling an electromechanically actuated gas-exchange valve that is equipped with a position sensor. Based on the position signal, a placement controller generates a drive signal for an output stage of the gas-exchange valve.
German Patent No. DE 38 06 969 A1 describes another electrohydraulic actuator for a gas-exchange valve, in which the valve-lifting curve is adjustable to a predefined setpoint-value characteristic, a travel sensor being provided which senses the position of the gas-exchange valve and supplies the position to a controller. It controls the current of a proportional magnet, which actuates a continuously adjustable control slide for regulating the hydraulic positioning force.
The conventional design approaches are based on the continuous, position-dependent regulation of a proportional drive variable, e.g., the current or the voltage of an output stage, whereby the force of the actuator and therefore the movement characteristic or the velocity of the gas-exchange valve is altered in the manner desired, in particular is regulated to a setpoint characteristic.
In the case of the EHVC system indicated, the basic requirement for a practical application or transfer of the conventional design approaches, i.e., for a regulation of the movement characteristic is not fulfilled, since a proportional driving and, hence, a positioning-force regulation is not possible as a matter of principle.
On the other hand, design approaches for controlling an EHVC actuator are known, which make use of an at least indirect feedback about the actuating characteristic. German Patent Application Nos. DE 10 2005 002 385 A1 and DE 10 2005 002 387 A1 describe adapting a lift control on the basis of a feedback about the positioning operations or adjusted valve lifts, in order to reduce or avoid control errors developing in response to a drift from actuator parameters.
Moreover, German Patent Application No. DE 10 2005 002 385 A1 also describes a regulation of the valve lift from cycle to cycle, which likewise starts out from a feedback about the valve lift. In that case, a correcting quantity, which is ascertained on the basis of positioning errors of preceding positioning operations, is added to a setpoint value of a driving duration of the control valve on the high-pressure side, the setpoint value being calculated based on a model.
The high modeling and/or application expenditure needed for the pure control is not substantially reduced in the above design approaches. In addition, errors in determining influence variables are not or are scarcely offset by an adaptation, and are only partially offset by a cycle-based regulation. Therefore, in spite of available feedback about the adjusted lifts, rapid changes of influence variables such as the oil pressure or of setpoint values of individual valve parameters almost unavoidably lead to noticeable transient deviations between actual and setpoint values of the valve lift.